A technique is known, in which a PM amount contained in an exhaust gas of an internal combustion engine is detected by a PM sensor. Patent Document 1 discloses a PM sensor (particulate sensor) provided with at least two electrodes. The PM sensor detects or senses a particulate deposition amount in the PM sensor from the measurement data of the electric characteristic including, for example, the AC impedance between the electrodes. Further, Patent Document 1 describes a technique in which the PM sensor is installed in particulate collecting means which collects PM on a part of a cross section perpendicular to a gas flow passage or on a second flow passage different from the gas flow passage.
Techniques, which relate to PM sensors, are also described in Patent Documents 2 to 5.